Rex Sole, Glyptocephalus zachirus
The Rex Sole, Glyptocephalus zachirus, whose common Spanish name is platija rey, is a member of the Righteye Flounder or Pleuronectidae Family, known collectively as platijas in Mexico. Globally, there are only three species in the genus Glyptocephalus, one of which is found in Mexican waters, this fish from of the Pacific.
The Rex Soles have elongated oval fusiform compressed bodies with a depth that is 29 to 33% of standard length. They are uniformly grayish light brown on their eyed-side and off-white on their blind side. Their head has a pronounced hump around the top eye and a small oblique mouth that ends before the modestly-sized and closely-set eyes. Their anal fin has 78 to 93 rays; their caudal fin is rounded; and their dorsal fin originates in the middle of the top eye and has 87 to 110 rays. They have exceedingly long pectoral fins on their eyed-side, a key to identification. They have a straight lateral line that is slightly curved over their pectoral fin and are covered with small scales.
The Rex Soles are found demersal over and within sandy and muddy bottoms at depths up to 3,700 feet. They reach a maximum of 60 cm (23 inches) length and 1.8 kg (4 pounds) in weight and are very slow growing. They are a migratory species found in shallow waters during the summer and in deeper waters in winter when spawning occurs. They are opportunistic well-camouflaged ambush predators that lie in wait half-submerged on the ocean floor consuming crustaceans (clams, crabs, polychaetes, and shrimp). They have a lifespan of up to 24 years.
In Mexican waters the Rex Sole have a limited distribution being found from Cedros Island northward along the central and northwest coasts of Baja.
The Rex Sole cannot be confused with any other species due to its exceedingly long pectoral fins.
The Rex Soles are fished commercially via trawler and comprise a major part of the flatfish trawl fishery north of California. They are heavily regulated; in the Bering Sea they are fished with special modified “Bering Sea Flatfish Gear” that consists of sweeps raised off the seafloor by bobbins spaced at 30-meter intervals to herd flatfish into relatively small nets. This technique dramatically reduces the adverse effects of fishing on seafloor habitat. Fish are processed on-board and immediately frozen, then processed further onshore. They have become an excellent substitute for the once common Sanddab as they have tender white finely-grained meat with a mild flavor. They are normally sold whole, fresh or frozen, or “pan ready” (with their head, innards, scales, tail, and fins removed as they are difficult to fillet). Many are processed into fertilizer. They are sold in great abundance in the ethnic fish markets of California. Some of the highly competitive San Diego based Asian markets have been known to substitute Flathead Sole, Hippoglossoides elassodon, for Rex Sole offering such “Rex Sole” at discounted prices. Efforts to farm this species have been unsuccessful primarily due to its slow growth.